This verse is addressed to a specific person, not the crowd, probably in the answer to a question. This is hidden in English because we cannot see the differences between the singular and plural "you". Also, the form of these if/then statement is something that probably will happen in the future.  The vocabulary here is very different from the Matthew version, though the sentiment is similar. This verse uses one word that is common in the Gospels, but that Jesus only uses himself here.

The word translated as "take heeds" means"hold to", "offer", "turn toward", "attend to", "pay attention," and "be on your guard against". Its root is the Greek word meaning "have" and "hold". It works somewhat like our phrase "hold fast". It is a command to the group of listeners.

 "To yourselves" is a special reflexive pronoun that means "himself", "herself," and so on.

The Greek word meaning "if " indicates more of an expectation of something happening than "if" alone. This is often how we use the word "when". 

The word translated as "thy" is the possessive form of the second person pronoun.

The word translated as "brother" means a biological brother, any kinsmen, and more broadly and friend or associate.

"Trespass" is from the verb which means "to miss the mark", "to fail in one's purpose", "to err", "to be mistaken," and "to neglect."  This is the verb translated as "sin" elsewhere. This same verb is used in the Matthew version.

The unique word here for Jesus is translated as "rebuke". The verb means  "to lay a value upon",  "to show honour to", to "raise in price",  of judges, "to lay a penalty on a person" and  to "censure".  Note that this word primarily means explaining the cost of something or the penalty for doing something. This word is frequently used in the NT to describe Jesus "rebuking" his followers, the weather, or a "demon" or "charging" someone to do or not to do something. We get the sense that it means "criticize" or "condemn" or "command" when it really doesn't. This idea is closer to the version in Matthew, which involves questioning him. 

The word translated as "him" is the Greek word commonly translated as third-person pronouns in English.  The word means "the same" when used as an adjective. In the adverbial form, it  means "just here" or "exactly there." 

The Greek word meaning "if might" indicates more of an expectation of something happening than "if" alone. This is often how we use the word "when".

The word translated as "repent" has nothing to do with sin or, generally, with religion or asking for forgiveness. The Greek word translated as "repent" has a primary meaning of to understand something after the fact, with the sense of seeing it is too late. Is specific meaning is to "understand afterward," as seeing the truth after a mistake is made. From this idea, it comes to mean to change your mind, shifting your perspective. This is in the form of a command.

The word translated as "forgive" primarily means "to let go", "to let drop", or "to send away." This same word is usually translated as "leave", "forgive", "suffer," and "let" in the New Testament.

The word translated as "him" is the Greek word commonly translated as third-person pronouns in English.  The word means "the same" when used as an adjective. In the adverbial form, it  means "just here" or "exactly there."